DESCRIPTION(Adapted from applicant's abstract): The objective is to develop a novel optical system for the in vitro assay of microbes which respire oxygen. It uniquely presents opportunities to assay for the presence or absence of viable organisms, monitor microbial metabolism, and conduct bioassays with microbes for toxic or stimulatory conditions. The method optically measures oxygen consumption in samples. It does not require insertion of probes or sensors into a sample or sample vessel, therefore it is practical for conducting rapid, economical, analyses of multiple samples. The approach innovatively uses oxygen sensitive indicator material in the assay sample. Spectral properties of the indicator change in an oxygen-concentration dependent manner. The oxygen content of samples is determined by spectral interrogation of indicators in vessels using an external optical reader. The aims of Phase I are to show the feasibility of reading indicator in vessels, tracking microbial oxygen consumption in vitro, and use of the system for bioassays with microbes. This will be done by producing sample vessels with indicator and with our optical system analyzing oxygen metabolism of microbes exposed to various conditions. The system will be versatile and useful for numerous applications ranging from clinical assays, toxicity tests, microbial research, and pharmaceutical development, to sterility tests. Its value towards developing bioassays employing microbes for toxicology and environmental assays has widespread potential.